Two main factors I see for giving Tony a win here:
1. They have full knowledge of each other
2. Tony has never faced an opponent like this
So, very little snarky discussion, very large amounts of missiles coming straight for Syndrome. We saw in Incredibles what happens when Syndrome gets taken by surprise by both his deathbot sphere thing in the city and Bob throwing a car at him. Iron Man has way more options than that robot or a thrown car.
Syndrome gets obliterated.